Common austenitic stainless steels contain a maximum by weight percent of 0.15% carbon, a minimum of 16% chromium and sufficient nickel and/or manganese to retain a face-centered-cubic (fcc) austenitic crystal structure at cryogenic temperatures through the melting point of the alloy. Austenitic stainless steels are non-magnetic non-heat-treatable steels that are usually annealed and cold worked. Common austenitic stainless steels are widely used in power generating applications; however, they are becoming increasingly less desirable as the industry moves toward higher thermal efficiencies by increasing the working temperatures of the generators. Austenitic stainless steels for high temperature use rely on Cr2O3 scales for oxidation protection. These scales grow relatively quickly, and do not function well in environments containing species like water vapor, sulfur, carbon, etc due to inherent limitations of the Cr2O3 scales formed on these alloys. Creep failure of common austenitic stainless steels such as types 316, 321, and 347 has limited the use of these steels at higher working temperatures.
There have been a number of approaches to improving oxidation resistance of austenitic steels for high temperature use as described in the patent application referenced above.